U.S. patent number 8,777,017 [Application Number 13/616,335] was granted by the patent office on 2014-07-15 for apparatus and method for filter cleaning by ultrasound, backwashing and filter movement during the filtration of biological samples.
This patent grant is currently assigned to Smith & Nephew, Inc.. The grantee listed for this patent is Stephen Curran. Invention is credited to Stephen Curran.
United States Patent |
8,777,017 |
Curran |
July 15, 2014 |
Apparatus and method for filter cleaning by ultrasound, backwashing
and filter movement during the filtration of biological samples
Abstract
The present application is directed to the separation of a solid
fraction from a fluid sample particularly a therapeutic cellular
fraction from a biological sample such as a bone marrow sample by a
porous filter which separates a filtration unit into an upper
pre-filtration chamber into which a fluid sample requiring cell
separation is introduced and a lower post-filtration chamber into
which a fluid capable of transmitting an acoustic standing wave is
introduced. An acoustic element is coupled to a substrate which is
located within and at the bottom of the lower chamber and which
resonates in response to the acoustic generating element and
generates a standing wave through the two fluid phases and the
filter to agitate the sample. Simultaneously, a cyclic process of
vacuum draw, causes movement of the sample downwards through the
filter. Vacuum pressure, fluid flow rate and frequency of vibration
are controlled from a remote unit housing appropriate pumps and
valves.
Inventors: |
Curran; Stephen (York,
GB) |
Applicant: |
Name |
City |
State |
Country |
Type |
Curran; Stephen |
York |
N/A |
GB |
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Assignee: |
Smith & Nephew, Inc.
(Memphis, TN)
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Family
ID: |
39509637 |
Appl.
No.: |
13/616,335 |
Filed: |
September 14, 2012 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20130098827 A1 |
Apr 25, 2013 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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12527561 |
Sep 25, 2012 |
8273253 |
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PCT/GB2008/000704 |
Feb 29, 2008 |
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Foreign Application Priority Data
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Mar 2, 2007 [GB] |
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0704180.9 |
Nov 15, 2007 [GB] |
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0722448.8 |
Feb 1, 2008 [GB] |
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0801901.0 |
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Current U.S.
Class: |
210/384;
210/748.05 |
Current CPC
Class: |
B01L
3/50255 (20130101); B01D 29/62 (20130101); C02F
1/34 (20130101); B01L 2400/0487 (20130101); C02F
2209/005 (20130101); B01L 2400/0436 (20130101) |
Current International
Class: |
C02F
1/34 (20060101) |
Field of
Search: |
;210/748.02,748.05,384,416.1,473 |
References Cited
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|
Primary Examiner: Prince; Fred
Attorney, Agent or Firm: Fox; David L. JL Salazar Law
Firm
Parent Case Text
RELATED APPLICATIONS
This application is a continuation of U.S. Ser. No. 12/527,561
filed on Jan. 25, 2010, now U.S. Pat. No. 8,273,253, issued Sep.
25, 2012, which is the U.S. national phase of International
Application No. PCT/GB2008/000704 filed on 29 Feb. 2008 published
in English on 12 Dec. 2008 as International Publication No. WO
2008/107652 A1, which application claims the priority to UK
provisional application No. 0704180.9 filed on 2 Mar. 2007, UK
provisional application No. 0722448.8 filed on 15 Nov. 2007 and UK
provisional application 0801901.0 filed on 1 Feb. 2008, all of
which are herein incorporated in their entirety.
Claims
The invention claimed is:
1. An apparatus for separating a specific cell fraction containing
mononuclear cells from a fluid sample containing a heterogeneous
mixture of cells having at least mononuclear cells and red blood
cells, the apparatus comprising a filtration unit, the filtration
unit comprising: at least one filter, which: (i) has pores capable
of separating the heterogeneous mixture of cells in the fluid
sample, comprising at least mononuclear cells and red blood cells,
into the specific cell fraction, having the mononuclear cells; and
(ii) divides the unit into a pre-filtration chamber for receiving
the fluid sample, and a post-filtration chamber for receiving a
fluid of the fluid sample and the at least red blood cells of the
heterogeneous mixture of cells in the fluid sample; a programmable
logic controller; an acoustic wave generating element capable of
generating an acoustic wave in at least one of the group consisting
of the fluid sample in the pre-filtration chamber, or the fluid of
the fluid sample in the post-filtration chamber; and a substrate
capable of attachment to the acoustic wave generating element.
2. The apparatus of claim 1, wherein the acoustic wave generated by
the acoustic wave generating element agitates at least one of the
group consisting of the fluid sample in the pre-filtration chamber,
the at least one filter, or the fluid of the fluid sample in the
post-filtration chamber.
3. The apparatus of claim 2, wherein there is a relationship
between a frequency of the acoustic wave generated by the acoustic
wave generating element and an amount of agitation of at least one
of the fluid sample in the pre-filtration chamber, the at least one
filter, or the fluid of the fluid sample in the post-filtration
chamber.
4. The apparatus of claim 1, wherein the programmable logic
controller is capable of controlling the frequency of an acoustic
wave generated by the acoustic wave generating element.
5. The apparatus of claim 1, wherein the at least one filter is
manufactured of a synthetic material.
6. The apparatus of claim 1, wherein the at least one filter
comprises a plurality of pores and wherein a pore diameter is
between about 1 and 12 microns.
7. The apparatus of claim 1, wherein the at least one filter is a
tracked etched filter and/or a nickel filter.
8. The apparatus of claim 1, wherein the at least one filter has a
thickness of about 11 to 50 microns.
9. The apparatus of claim 1, wherein the at least one filter
comprises a pore density of about 400,000 pores/cm.sup.2.
10. The apparatus of claim 1, wherein the at least one filter
comprises a plurality of pores and wherein a pore geometry is
selected from the group consisting of circular, ellipsoidal,
square, rectangular, or triangular.
11. The apparatus of claim 1, further wherein the pre-filtration
chamber of the filtration unit is divided into multiple chambers
capable of receiving batch fluid samples presented as a well plate
format.
12. An apparatus for separating a specific cell fraction from a
fluid sample containing a heterogeneous mixture of cells, the
apparatus comprising a filtration unit, the filtration unit
comprising: i. the fluid sample containing the heterogeneous
mixture of cells comprising at least mononuclear cells and red
blood cells; ii. the specific cell fraction having mononuclear
cells; iii. at least one filter having pores to separate the
heterogeneous mixture of cells into the specific cell fraction, the
at least one filter dividing the unit into a pre-filtration chamber
for receiving the fluid sample and a post-filtration chamber for
receiving fluid of the fluid sample and the at least red blood
cells of the heterogeneous mixture of cells of the fluid sample;
iv. an acoustic wave generating element capable of generating
acoustic waves capable of causing agitation in at least one of the
fluid sample, the at least one filter, or the fluid of the sample
in the post-filtration chamber; v. a substrate capable of
attachment to the acoustic wave generating element; and vi. a
pressure system capable of backflushing the filter by positive
pressure in the post-filtration chamber, or drawing the fluid of
the fluid sample and the at least red blood cells of the
heterologous mixture of cells of the fluid sample into the
post-filtration chamber by negative pressure in the post-filtration
chamber.
13. The apparatus of claim 12, further comprising a programmable
logic controller capable of controlling the pressure system.
14. The apparatus of claim 12, wherein the positive pressure in the
post-filtration chamber is in the range of about +0.1 to +0.5
psi.
15. The apparatus of claim 12, wherein the positive and/or negative
pressure in the post-filtration chamber is in the range of about
-0.5 to +0.5 psi.
16. The apparatus of claim 12, wherein the positive pressure and
the negative pressure in the post-filtration chamber alternate in a
cyclic manner with a net negative pressure in the post-filtration
chamber and a net reduction in volume of the fluid sample in the
pre-filtration chamber following a cycle.
17. The apparatus of claim 12, further comprising a vacuum
pump.
18. The apparatus of claim 12, further comprising a backflushing
fluid for backflushing the at least one filter.
19. An apparatus for separating a specific cell fraction containing
mononuclear cells from a fluid sample containing a heterogeneous
mixture of cells having at least mononuclear cells and red blood
cells, the apparatus comprising a filtration unit, the filtration
unit comprising: at least one filter, which: (i) has pores capable
of separating the heterogeneous mixture of cells in the fluid
sample, comprising at least mononuclear cells and red blood cells,
into the specific cell fraction, having the mononuclear cells; and
(ii) divides the unit into a pre-filtration chamber for receiving
the fluid sample, and a post-filtration chamber for receiving a
fluid of the fluid sample and the at least red blood cells of the
heterogeneous mixture of cells in the fluid sample; a programmable
logic controller; an acoustic wave generating element capable of
generating an acoustic wave in at least one of the group consisting
of the fluid sample in the pre-filtration chamber, or the fluid of
the fluid sample in the post-filtration chamber; a substrate
capable of attachment to the acoustic wave generating element; and
an agitation element capable of agitating at least one of the group
consisting of the fluid sample in the pre-filtration chamber, the
at least one filter, or the fluid of the fluid sample in the
post-filtration chamber.
20. The apparatus of 19, wherein the agitation element is selected
from the group consisting of an impeller or other insert capable of
movement to agitate the fluid sample within the pre-filtration
chamber, a wall defining the pre-filtration chamber capable of
rotating to agitate the fluid sample within the pre-filtration
chamber, a wall defining the pre-filtration chamber and comprising
baffles and capable of rotating to agitate the fluid sample within
the pre-filtration chamber, or an at least one filter holder
capable of vibrating the at least one filter in a vertical
direction, a lateral direction, or a combination thereof.
21. The apparatus of 19, wherein the substrate comprises at least
one material selected from the group consisting of metals,
ceramics, and polymers.
Description
FIELD OF THE INVENTION
The present invention concerns the separation of a solid fraction
from a fluid sample. In particular the invention relates to
apparatus and methods for the separation of a therapeutic cellular
fraction from a biological sample, such as a bone marrow
sample.
BACKGROUND OF THE INVENTION
Progenitor cells have multi-lineage potential when differentiated
and therefore potentially lend themselves to a diverse range of
therapeutic treatments. It is conceived that an enriched fraction
of these cells delivered to a diseased or damaged tissue site may
have maximum therapeutic benefit through accelerated tissue
healing. Progenitor cells are typically a very rare population of
cells (Caplan 2005) contained within a heterogeneous mixture of
non-therapeutic cells in some mammalian tissues and fluids.
Various techniques and devices to capture cells have been reported
in the literature including sedimentation (Takazawa &
Tokashiki, 1989), centrifugation (Apelman et al, 1992; Jaeger,
1992) spin filters (Himmerlflab et al 1969) and cross-flow
microfiltration (Maiorella et al 1991). However, these are
associated with a number of disadvantages. Sedimentation processes
suffer from low sedimentation velocity of cells and a slow
separation process. Centrifugation devices rely on a radial force
to drive cells outwards from the fluid and although high recovery
is quickly achieved these devices typically have a high capital
cost associated with them. In addition, high shear stresses could
potentially damage cells or induce unwanted changes in e.g.
progenitor cells. Spin filters and cross-flow filters use membranes
to filter the cell suspension and these are susceptible to fouling
with subsequent loss in performance. Other processes using such
filters include controlled shear filtration (Vogel and Kroner,
1999), tangential flow filtration (Radlett, 1972) and dynamic
filtration. The rate and efficiency of separation is dependent on
the degree of fouling. Dynamic filtration relies on relative motion
between the membrane and the housing to generate a shear flow
independent of flow across the filter (Castilho & Medrohno,
2002). Vortex flow filters and rotating disc filters are the two
common types of dynamic filtration devices (Stromberg et al, 1989).
Karumanchi et. al. (2002) have provided a review of field-assisted
separation techniques for cells and biomacromolecules which include
electric, magnetic and acoustic phenomena to achieve the desired
separation. Dielectrophoresis is the lateral motion of uncharged
particles due to the polarization effect produced by non-uniform
electric fields (Docoslis et al, 1997, 1999). This is applicable
only to very low electrical conductivity media otherwise excessive
heating of the fluid will occur. Magnetic separations fall into two
types. In the first, the cells to be separated have an intrinsic
magnetic property (eg. red blood cells, magnetotactic bacteria) and
in the second type the non-magnetic component of the mixture that
are required must be rendered magnetic by a magnetic-responsive
entity. In both cases the fluid must be subjected to a magnetic
field to achieve separation. Magnetic separation has been used
extensively for numerous cell separations including bone marrow
processing to enrich for progenitor cells (Roath et al, 1990).
Acoustic separators have been widely used to separate
micro-organisms and cells but almost universally rely on using
ultrasonic waves. Ultrasonic cell retention is achieved due to the
formation of standing waves when an ultrasonic wave is reflected in
the direction opposite to the propagation of the wave. Cells become
trapped in the pressure node planes of the standing wave. Kilburn
et al, (1989) and WO95/001214, first reported the possibility of
using these waves as a means to separate cells from suspension and
many other reports using this technique have been reported since
(Coakley et al, 1994; Dobelhoof-Dier, 1994; Gaida et al, 1996;
Gorenflo et al, 2003, 2004). Ultrasonic separators require careful
tuning and typically have a limited loading capacity whereby only a
small volume of cells is recovered. In addition this technique is
used to remove a homogeneous population of cells from the fluid
phase and therefore cannot capture a specific population from a
heterogeneous mixture.
The present invention is directed towards apparatus and methods for
separating a solid fraction from a fluid sample. In particular the
present invention is directed to the separation of a cell fraction
from a heterogeneous mixture of cells within a fluid sample. The
process is a single step process with the cell separation being
based upon the mechanical filtration of a sample using only
physical means.
BRIEF SUMMARY OF THE INVENTION
According to an aspect of the invention there is provided apparatus
for separating a solid fraction from a fluid sample, the apparatus
comprising a filtration unit, the filtration unit comprising;
an acoustic wave generating element;
at least one filter which divides the unit into a pre-filtration
chamber for receiving the fluid sample and a post-filtration
chamber for receiving a fluid capable of transmitting acoustic
waves; and
a substrate configured to be associated with post-filtration
chamber, the substrate being capable of resonation upon application
of an acoustic wave thereto;
wherein the acoustic wave generating element is configured to be
associated with the substrate such that the acoustic wave
generating element causes resonation of the substrate which in turn
transmits an acoustic standing wave through both the fluid within
the post-filtration chamber and the fluid sample within the
pre-filtration chamber.
The transmission of an acoustic standing wave through the fluids
within the filtration unit results in the agitation of the fluids,
either continuously or in a pulsed manner, during the separation
process. A particular advantage of this agitation is that it
minimizes the fouling and clogging of the filter.
In embodiments of the invention in which the apparatus is being
utilised to separate a cellular fraction from a fluid sample, the
agitation of the fluids in the unit has a further advantage in that
it minimizes the contact time or residence time of the cells within
the pre-filtration chamber with the filter. This is desirable
because if the cells are in contact with or sufficiently adjacent
to the surface of the filter there is tendency for the cells to be
forced through pores under the pressure of the surrounding fluid.
Such passage through the pore is achievable by the deformation of
the cell, but during the passage the cells may be exposed to
undesirable stresses, such as shear stress, which may have
deleterious effects on the cell. In particular it has been shown
that white cell function can be significantly affected by shear
stresses (Carter et al, 2003). It is therefore desirable to prevent
the cells of interest from passing through the filter. In this
regard the filter is designed to allow the passage of fluid and
other cellular fractions while retaining the cells of interest in
the pre-filtration chamber.
An acoustic wave generating element is defined as a structure that
can generate an acoustic wave field in response to a power signal.
For example, in the case of a simple speaker, the power signal will
physically deflect a diaphragm at a defined amplitude and frequency
to generate the acoustic wave. Other acoustic elements include
piezoelectric transducers that generate vibrational energy in
response to applied AC voltages and the physical vibration is
transferred to the fluid as an acoustic force. Examples of
piezoelectric elements are ceramic discs with metal film electrodes
on each side, these thin piezoelectric films are typically
zinc-oxide.
The association of an acoustic wave generating element with a
substrate capable of resonation has a number of advantages over the
use of an acoustic element alone. The acoustic element is not in
direct contact with the fluid as this element is designed to
provide improved resonance when attached to a substrate material
which has a much larger area than the cone of the element itself.
This means more energy can be delivered to the fluid while still
using a small acoustic element. Overall this significantly improves
energy efficiency and footprint of the device, which is
particularly advantageous when processing large fluid volumes. A
suitable acoustic element can be obtained from NXT Technology
Limited (Hong Kong), Model No. RM-ETN0033K19C-2K01.
In embodiments of the invention the acoustic wave generating
element generates an acoustic standing wave having a frequency in
the range of between about 300-700 Hz. A relationship exists
between the fluid volume and the optimal frequency required.
Therefore, advantageously in particular embodiments of the
invention the user can input the volume of the fluid sample and the
frequency of the acoustic standing wave will be calculated. For
example, for a sample having a volume of between about 5 ml to 15
ml, the optimal frequency of the acoustic standing wave is between
about 300 Hz to 700 Hz.
In a specific embodiment of the invention the acoustic wave
generating element is a speaker having a power of 0.4 W, resistance
of 4 Ohm, amplitude in the range of between about 4.2V to 7.36V
peak to peak and a frequency range in the range of between about
300-700 Hz.
In embodiments of the invention the substrate is located
substantially parallel to the filter.
In embodiments of the invention the substrate is located at the
base of the filtration unit.
The substrate can be made of any suitable material which is capable
of resonation in response to stimulation by the acoustic generating
element. For example, a metal, a ceramic or a polymer.
Advantageously, because the substrate may come into contact with
the fluid used in the apparatus the substrate is made of medical
grade material. This reduces the risk of any toxic substance
contamination.
In embodiments of the invention the acoustic wave generating
element is reversibly coupled to the substrate. This coupling can
be achieved by a variety of means available to the man skilled in
the art, for example the use of an adhesive. This is particularly
advantageous if the filtration unit is designed to be disposable,
because the acoustic element can be uncoupled and re-used on other
units.
The movement of the fluid sample across the filter can be via
passive movement resulting from gravitational forces. Alternatively
the fluid sample can be actively moved across the filter by the
application of a positive or a negative pressure. The flow rate of
the fluid sample across the filter can be constant or variable.
In embodiments of the invention the fluid provided within the
post-filtration chamber which is capable of transmitting an
acoustic wave also acts as a washing fluid. In this embodiment, a
positive pressure pump is provided which pushes the washing fluid
from the post-filtration chamber through the filter to the
pre-filtration chamber. At the same time a negative pressure pump
is drawing fluid from the pre-filtration chamber to the
post-filtration chamber. Thus, the fluid sample and the washing
fluid are sequentially moved in opposing directions across the
filter such that the net movement of the fluid sample is into the
post-filtration chamber and the separated solid fraction is
retained in the pre-filtration chamber.
The sequential movement of the fluid sample and the washing fluid
in opposing directions across the filter prevents fouling and
clogging of the filter, further increasing the efficiency of the
separation process. This sequential movement can be cyclical, with
one phase of the cycle being the rapid back-flushing of the filter
using the washing fluid and the second phase of the cycle being the
forcing of fluid sample downwards through the filter. This cyclic
process is continued in order to sufficiently reduce the sample
volume while also retaining a sufficient volume of fluid above the
filter such that the particulate fraction is retained in solution.
Typically the sample volume is reduced by about 10-fold.
In further embodiments of the invention the filter itself is
agitated during the separation process. This agitation can be
achieved, for instance, by associating the filter with a moveable
holder. Agitation can be in a vertical direction or a lateral
direction or a combination thereof. In alternative embodiments of
the invention the filter can be rotated.
Other means of additionally agitating the washing fluid and/or the
fluid sample include using a rotating element (eg. impeller or
insert in the fluid), rotating the walls of the chamber, or
rotating the walls of the chamber, wherein the walls of the chamber
are provided with baffles or the use of an active chip.
A "fluid sample" is any fluid from which solid components are to be
separated. A sample can be from any source, such as an organism,
group of organisms from the same or different species, from the
environment such as from a body or water or from the soil, or from
a food source, or an industrial source. A sample can be a processed
or unprocessed sample. A sample can be a gas or a liquid. A sample
can be an extract, for example a liquid extract of a soil or food
sample.
The apparatus is particularly suitable for liquids that are viscous
and which have a higher tendency to foul the filter by forming a
film or coat on the surface of the filter. Back-washing of washing
fluid through the filter, and optionally the agitation of the fluid
sample and/or the filter significantly reduces the fouling of the
filter and also maintains the particulate fraction in solution in
the pre-filtration sub-chamber.
The sample can be obtained from a subject. The subject can be any
organism, such as an animal or a human. An animal can include any
animal, such as a feral animal or domestic animal. A domestic
animal can include for example a companion animal such as a dog or
cat.
The sample can be a biological sample such as a blood sample, an
effusion, a urine sample, semen, bone marrow aspirate, spinal
fluid, a cell suspension from tissue, mucus, sputum or saliva. The
biological sample can be obtained from any animal and is not
limited to a biological sample from humans.
A "blood sample" as used herein refers to a processed or
unprocessed blood sample, including cord blood samples, bone marrow
aspirates, internal blood or peripheral blood and can be of any
volume and can be from any subject such as an animal or human. A
preferred subject is human.
The solid fraction to be separated from the biological fluid sample
can comprise at least one cell fraction. The cell fraction
preferably comprises a therapeutic cell, that is any cell that can
have therapeutic or curative effects.
The cell fraction can comprise or consist of at least one white
blood cell. A "white blood cell" is a leukocyte or a cell of
hematopoietic lineage that is not a reticulocyte or platelet and
which can be found in the blood of an animal or human. Leukocytes
can include natural killer cells ("NK cells"), and lymphocytes such
as B lymphocytes ("B cells") or T lymphocytes ("T cells").
Leukocytes can also include phagocytic cells such as monocytes,
macrophages, and granulocytes, including basophils, eosinophils and
neutrophils. Leukocytes can also include mast cells.
The cell fraction can comprise or consist of at least one red blood
cell. A "red blood cell" is an erythrocyte.
The cell fraction can comprise or consist of at least one
neoplastic cell. A "neoplastic cell" refers to abnormal cells that
have uncontrolled cellular proliferation and continue to grow after
the stimuli that induced the new growth has been withdrawn.
Neoplastic cells tend to show partial or complete lack of
structural organization and functional coordination with the normal
tissue, and may be benign or malignant.
The cell fraction can comprise or consist of at least one malignant
cell. A "malignant cell" refers to a cell having the property
locally invasive and destructive growth and metastasis. Examples of
malignant cells include, but are not limited to; leukemia cells,
lymphoma cells, cancers cells of solid tumors, metastatic solid
tumor cells (e.g. breast cancer cells, prostate cancer cells, lung
cancer cells, colon cancer cells) in various body fluids including
blood, bone marrow, ascistic fluids, urine, bronchial washes.
The cell fraction can comprise or consist of at least one cancerous
cell. A "cancerous cell" refers to a cell that exhibits deregulated
growth and, in most cases, has lost at least one of its
differentiated properties, such as, but not limited to,
characteristic morphology, non-migratory behavior, cell-cell
interaction, and cell-signaling behavior, protein expression and
secretion pattern etc.
The cell fraction can comprise or consist of at least one stem
cell. A "stem cell" is an undifferentiated cell that can give rise,
through one or more cell division cycles, to at least one
differentiated cell type.
The cell fraction can comprise or consist of at least one
progenitor cell. A "progenitor cell" is a committed but
undifferentiated cell that can give rise, through one or more cell
division cycles, to at least one differentiated cell type.
Typically a stem cell gives rise to a progenitor cell through one
or more cell divisions in response to a particular stimulus or set
of stimuli and a progenitor gives rise to one or more
differentiated cell types in response to a particular stimulus or
set of stimuli.
Bone marrow (or medulla ossea) is the soft tissue found in the
hollow interior of bones. There are two types of bone marrow: red
marrow (also known as myeloid tissue) and yellow marrow. Red blood
cells, platelets and most white blood cells arise in red marrow;
some white blood cells develop in yellow marrow.
Bone marrow contains two types of stem cells: hematopoietic stem
cells and mesenchymal stem cells. Stem cells are primal cells
common to all multi-cellular organisms that retain the ability to
renew themselves through cell division and can differentiate into a
wide range of specialized cell types. Hematopoietic stem cells give
rise to the three classes of blood cell that are found in the
circulation: white blood cells (leukocytes), red blood cells
(erythrocytes), and platelets (thrombocytes). Mesenchymal stem
cells are found arrayed around the central sinus in the bone marrow
and have the capability to differentiate into osteoblasts,
chondrocytes, myocytes, and many other types of cell.
While embryonic stem cells are true stem cells in that they are
totipotent or pluripotent and show unlimited capacity for
self-renewal, the adult stem cells within the bone marrow are more
appropriately termed progenitor cells, which like stem cells have a
capacity for self-renewal and differentiation, although far more
limited. Progenitor cells are usually unipotent or multipotent
rather than pluripotent.
Mesenchymal stem cells or MSCs, classically obtained from bone
marrow are multipotent stem cells that can differentiate into a
variety of cell types. Cell types that MSCs have been shown to
differentiate into include osteoblasts, chondrocytes, myocytes,
adipocytes, neuronal cells.
Bone marrow density can and does vary from patient to patient and
there is no uniform viscosity to bone marrow. Younger patients
often have a denser thicker marrow the result of more trabecular
tissue in the cavity. This viscous marrow has a tendency to foul
the filters within separation devices.
In embodiments of the invention the fluid sample is a bone marrow
aspirate.
In further embodiments of the invention the fluid sample is a bone
marrow aspirate and the solid fraction is a progenitor cell.
A "tissue" as used herein includes the four basic types of tissue
present in all animals: epithelium, connective tissue, muscle
tissue and nerve tissue.
Examples of connective tissue include skin, muscle, cartilage,
bone, tendon, ligament, joint capsule and adipose tissue.
"Adipose tissue" as used herein is intended to mean fat and other
sources of microvascular tissue in the body. Adipose tissue is a
complex tissue containing multiple cell types including adipocytes,
pericytes, fibroblasts, macrophages, stem cells and microvascular
cells. As such adipose tissue is one of the most convenient sources
of precursor cells in the body.
"Microvascular cells" as used herein is intended to mean cells
which comprise the structure of the microvasculature, such as
endothelial cells, smooth muscle cells and pericytes.
Adipose tissue can be harvested from an "adipose" depot within the
body. Suitable depots include the epididymis, the interscapular fat
pad or the infrapatellar fat pad (Hoffas fat pad). Alternatively,
and potentially more conveniently, the adipose tissue can be a
lipoaspirate resulting from a liposuction procedure.
While a lipoaspirate can be directly introduced into the device of
the present invention, fragments of adipose tissue require
pre-processing. The tissue fragments are comminuted and/or
enzymatically digested to release the cellular component of the
tissue. This cellular component can then be suspended in a suitable
carrier and introduced into the device.
It is envisaged that the lipoaspirate and/or cell suspension
obtained above can undergo further processing prior to introduction
into the device. For example, gravitational sedimentation and/or
centrifugation can be used to separate large fat globules and
adipocytes from the stromal fraction (comprising stem cells,
endothelial cells and pericytes).
In embodiments of the invention in which a biological sample is
being filtered the filtration unit can be coupled to an aspirator
such that the fluid is transferred directly from the subject into
the filtration unit. The filtration unit can be used in a sterile
environment and this arrangement reduces the risk of contamination
of the sample between removal of the sample from the patient and
introduction into the filtration unit.
In alternative embodiments of the invention the solid fraction can
consist of an etiological agent such as bacteria, fungus,
protozoan, virus, parasite or prion that can infect a subject.
The sample can be an in vitro cell suspension.
The filter, which can also be referred to as a foil, can be
manufactured of any material suitable for separating a solid
fraction from a fluid sample in the method described in the present
invention. The filter can be manufactured from a natural or a
synthetic material or a combination thereof. Suitable materials,
include, but are not limited to metals, metal alloys, ceramics or
polymeric materials. Examples include polycarbonate (PLC),
polyethylene terephthalate (PET), polyidide (PI), nickel and
stainless steel. The materials are preferably medical grade
materials. Suitable tracked etched filters are available from it4ip
(Belgium). Suitable nickel foil filters are available from Tecan
Limited (U.K.).
In embodiments of the invention the filter is substantially planar.
That is to say, the filter has a 2-dimensional profile wherein the
diameter of the filter is greater than the height of the filter.
Such a profile increases the potential surface area by which the
filter is exposed to the fluid sample, thereby increasing the rate
of filtration. The profile also minimizes the potential for any
solid matter to become clogged within the filter.
Examples of suitable thickness for the filter are 11, 23 and 50
microns. The thinner the filter the faster the rate of flow of
fluid therethrough.
It is envisaged that filter can be provided with pores of the same
diameter or varying diameter having the same geometry.
Alternatively, the filter can be provided with pores of the same
diameter with varying geometry. Alternatively still the filter can
be provided with pores of varying diameter and varying geometry
Suitable pore geometries include, but are not limited to, circular,
ellipsoidal, square, rectangular or triangular in lateral
cross-section.
The pores can be tapered. Tapering of the pores facilitates
deformation of the cells under vacuum. Depending on the size of the
pore at each end of the taper and the orientation of the taper,
preferential selection of cells based on size can be achieved. In
advantageous embodiments of the invention the narrowest point of
the tapered pore is located at the upper surface of the filter.
This arrangement allows smaller cells to flow through the pore
whilst larger cells are retained above the filter. Conversely, it
seems to make it more difficult during the backwash of washing
fluid upwards through the filter for the cells in the
post-filtration chamber to return through pores. It has been found
that if the narrowest point of the pore is located at the lower
surface of the filter cells have a tendency to enter the pore and
deform in order to squeeze through the narrowest point.
In particular embodiments of the invention the pores have a
diameter range of between about 1 micron and 12 micron.
In further embodiments of the invention the pores can be
cylindrical in shape.
In further embodiments of the invention in which progenitor cells
are separated from a bone marrow aspirate, a suitable filter is
made of PET, has, a thickness of 23 microns, a pore diameter of 3
microns and a pore density of 400,000 pores per cm.sup.2. The
optimal negative pressure generated by a vacuum pump to effectively
"pull" the fluid through the filter is in the range of about -0.1
to -0.5 psi, more specifically -0.2 to -0.3 psi. Alternatively a
positive pressure can be generated to effectively "push" the fluid
through the filter. The optimal positive pressure generated by such
a pump is in the range of about +0.1 to +0.5 psi, more specifically
+0.2 to +0.3 psi.
The design of the filtration unit can be modified such that the
aspect ratio of the pre-filtration chamber for the fluid sample is
reduced thereby providing a larger surface area for filtration per
unit volume.
In further embodiments of the invention, the pre-filtration chamber
of the filtration unit is divided into multiple chambers that can
be used to receive batch fluid samples presented as a well plate
format.
Following filtration the remaining fluid sample, which comprises
the separated (also referred to as a purified, enriched or
concentrated) solid fraction, can be removed from the upper chamber
of the filtration unit by suction, for example using a pipette and
either stored or utilized. In other embodiments of the invention,
particularly in embodiments in which the remaining fluid sample
comprises a therapeutic cell fraction, the remaining fluid sample
can be mixed with, for example, a hydrogel or a bone cement. In
these embodiments the hydrogel or bone cement functions as a cell
repository.
According to an aspect of the invention there is provided a method
of separating a solid fraction from a fluid sample, said method
comprising the steps of;
i) introducing a fluid sample into the apparatus of the present
invention;
ii) filtering the fluid sample; and
iii) removing the separated fraction from the pre-filtration
chamber.
According to a further aspect of the invention there is provided a
method of isolating or separating a therapeutic cell from a fluid
sample using apparatus of the present invention.
In embodiments of the invention the fluid, sample can be a
biological sample such as a blood sample, an effusion, a urine
sample, semen, bone marrow aspirate, spinal fluid, a cell
suspension from tissue, mucus, sputum or saliva.
In embodiments of the invention the therapeutic cell is a
progenitor cell.
According to a further aspect of the invention there is provided a
method of isolating or separating a therapeutic cell from a bone
marrow aspirate using apparatus of the present invention.
In embodiments of the invention the therapeutic cell is a
progenitor cell.
The system can be operated manually. However, in order to improve
the overall efficiency and accuracy of the separation process,
particularly when the apparatus is used in an operating room
situation by medical staff, the apparatus is advantageously
automated. A Programmable Logic Controller (PLC) can be programmed
to switch a vacuum pump and a backwashing pump on and off in cyclic
rotation in a timed sequence. The vacuum pump draws the fluid
sample downwards through the filter under negative pressure. The
backwashing pump forces washing fluid upwards through the
filter.
The filtration chamber and/or the filter can be disposable. The
control unit can be disposable or a standalone dedicated unit.
In a further aspect of the invention the isolated therapeutic
cell(s) can be directly administered as a suspension into a site in
need thereof. Alternatively, the cells can be combined with or
associated with an appropriate carrier material, for example, a
gel, a paste, a cement, a glue, a scaffold, a film, an implant or a
dressing.
It is envisaged that the isolated therapeutic cells can be utilized
in a range of medical applications, for humans and/or non-human
animals to repair, regenerate and/or augment tissue function.
Examples of medical applications include orthopaedic, neurological,
cardiovascular, dermatology, cosmetic surgery and dental.
It is envisaged that in certain embodiments of the invention the
isolated therapeutic cells comprise mesenchymal stem cells. These
cells are capable of differentiation into osteoblasts,
chondrocytes, myocytes and adipocytes. A therapeutic fraction
comprising mesenchymal stem cells can be used in orthopaedic
indications, resulting from disease or injury, such as cartilage
repair, bone repair (including fracture repair), spinal fusion,
degenerative disc treatment (including annulus repair, nucleous
populous augmentation, disc augmentation).
Functional endothelial progenitor cells (EPCs) are central to
vasculogenesis and angiogenesis. EPCs have been shown to develop
from bone marrow mononuclear cells in adult animals. It is
therefore envisaged that in certain embodiments of the invention
the isolated therapeutic cells comprise EPCs and this therapeutic
fraction can be used in indications in which damaged or ischemic
tissue requires repair, regeneration or vasculogenesis, such as
peripheral vascular disease.
There is therefore provided methods for i) forming new blood
vessels in a tissue in a subject, ii) increasing blood flow in a
tissue in a subject, iii) treating diseased tissue in a subject,
iv) increasing angiogenesis in a diseased tissue or v) preventing
heart failure in a subject, all of said methods comprising the
steps of;
a) isolating bone marrow mononuclear cells using the apparatus
according to the present invention,
b) transplanting locally into the tissue an effective amount of the
bone marrow mononuclear cells so as to form new blood vessels in
the tissue.
In embodiments of the invention the bone marrow mononuclear cells
are autologous.
The tissue into which the bone marrow mononuclear cells are
transplanted includes and diseased or damaged tissue and any tissue
in need of repair or regeneration, including but not limited to
underpurfused tissue such as tissue found in chronic ischemia, and
also cardiac muscle tissue, skeletal muscle tissue, brain tissue
e.g affected by stroke or AV malformations, coronary vessels,
kidney, liver, organs of the gastrointestinal tract, muscle tissue
afflicted by atrophy, including neurologically based muscle
atrophy.
In embodiments of the invention the new blood vessels are
capillaries and/or collateral blood vessels.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described below with reference to the
accompanying drawings, in which:
FIG. 1: A schematic showing the general operating principle of the
apparatus of the invention.
FIG. 2: A schematic representation of an embodiment of apparatus of
the invention in which the fluids in the pre- and post-filtration
chambers are sequentially moved across the filter.
FIG. 3: A drawing showing the control unit.
FIG. 4: A drawing showing the filtration unit.
FIG. 5: A drawing showing the filtration unit connected to the
control unit.
FIG. 6: A drawing showing the acoustic wave generating element
FIG. 7: Vibrating filter holder for use within the filtration
unit.
FIG. 8: Average enrichment of mononuclear cells (MNCs) from porcine
whole blood using filters of a given mean pore size within the
apparatus of the present invention (n=6).
FIG. 9: Processing time for enrichment of MNCs from whole porcine
blood using filters having a mean pore size of about 2.9 micron
within apparatus of the present invention (n=3).
FIG. 10: Volume reduction of porcine bone marrow tissue over 8
minutes for varying operational conditions using apparatus of the
present invention. The apparatus uses a filter having a mean pore
size of about 3 micron and a flow rate of 6 drops/min.
FIG. 11: Optimized flow-rate across the filter by restricting the
vacuum pressure with an in-line needle valve.
FIG. 12: The fold increase in white blood cells and red blood cells
using apparatus of the present invention.
FIG. 13: The ratio of white blood cells to red blood cells within a
whole porcine blood sample pre- and post-filtration using apparatus
of the present invention.
FIG. 14: Data using separation apparatus shows a volume reduction
up to and beyond 10-fold can be achieved with >90% recovery of
mononuclear cells. The volume reduction and concentration of
mononuclear cells are linearly related. Typical processing time is
less than 10 minutes.
FIG. 15: Representative profile of the pore size distribution
within a PET filter for separation of mononuclear cells from
porcine BMA.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1: A schematic showing the general operating principle of the
apparatus of the invention in which the following reference
numerals refer:
1. Filtration unit
2. Porous filter
3. Upper (pre-filtration) chamber for receiving fluid sample
4. Fluid sample
5. Lower (post-filtration) chamber for receiving back-flushing
fluid
6. Fluid provided in the post-filtration chamber
7. Resonating substrate
8. Acoustic wave generating element
9. Vacuum draw (optional)
The porous filter 2 separates a filtration unit 1 into two
chambers; an upper (pre-filtration) chamber 3 into which a fluid
sample 4 requiring cell separation is introduced and a lower
(post-filtration) chamber 5 into which a fluid 6 capable of
transmitting an acoustic standing wave is introduced. An acoustic
element 8 is coupled to a substrate 7 which is located within and
at the bottom of the lower chamber and which resonates in response
to the acoustic generating element and generates a standing wave
through the two fluid phases and the filter to agitate the sample.
Simultaneously, a cyclic process of vacuum draw 9 causes movement
of the sample downwards through the filter. Vacuum pressure, fluid
flow rate and frequency of vibration are controlled from a remote
unit housing appropriate pumps and valves. A concentrated fraction
of desired larger cells is retained on top of the filter while
smaller cells pass through the filter to a waste receptacle (not
shown).
In a specific embodiment of the invention the acoustic element is a
speaker having a power of 0.4 W, resistance of 4 Ohm, amplitude in
the range of between about 4.2V to 7.36V peak to peak and a
frequency range in the range of between about 300-700 Hz.
FIG. 2: A schematic representation of an embodiment of apparatus of
the invention in which the fluids in the pre- and post-filtration
chambers are sequentially moved across the filter, and in which the
following reference numerals refer
10. Filtration unit
11. Porous filter
12. Receptacle for receiving evacuated fluid from filtration
unit
13. Receptacle for receiving backwashing fluid
14. Backwashing pump
15. Vacuum pump
16. Acoustic wave generating element/resonating substrate
17. Solenoid valve (back-flushing line)
18. Solenoid valve (vacuum line)
19. PLC digital control unit and display
20. Needle valve
This figure illustrates an apparatus which comprises the filtration
unit of the invention (as illustrated in FIG. 1) and a control
unit. A PLC controller (Mitsubuishi AL2-24MR-04) in the control
unit 19 can be programmed to switch the vacuum pump 15 and
back-flushing pump 14 (both Koge KPV14A-6A) on and off. It is also
used to control the triggering of solenoid valves (Cole Parmer
98302-02) 17 and 18. This can be programmed to run the valves and
pumps in a timed sequence or to control the pumps manually. An
amplifier and signal generator chip built into the control unit
allows the frequency and amplitude of the acoustic element 18 to be
set via the PLC. A receptacle to collect evacuated fluid from the
device 12 and a receptacle to deliver back-flushing fluid 13 are
connected to the filter unit and control unit with appropriate flow
tubes.
FIG. 3: A drawing showing the control unit in which the following
reference numerals refer:
21. PLC unit housed in control box
22. control keypad
23. device on/off
24. vacuum line solenoid control
25. acoustic element on/off
26. vacuum manual override
27. backflush manual override
28. acoustic frequency control
29. acoustic element amplitude control
30. acoustic element frequency indicator
31. drip event indicator LED
FIG. 4: A drawing showing illustrating the component assembly of
filtration unit of the invention in which the following reference
numerals refer:
32: upper chamber
33. middle chamber
34. clamps to secure upper chamber and middle chambers
35. membrane filter
36. O-rings sealing to filter when the upper and middle chambers
are clamped together
37. upper tissue sample reservoir within middle chamber
38. input into saline reservoir below filter
39. lower chamber
40. acoustic element
41. O-rings sealing to acoustic element
42. exit for acoustic element electrical connection
FIG. 5: A drawing showing the filtration unit connected to the
control unit in which the following reference numerals refer:
43. filtration unit
44. vacuum line from filtration unit to vacuum pump
45. vacuum pump
46. vacuum solenoid
47. vacuum line to waste chamber
48. waste chamber
49. backflush line to filtration unit
50. backflush pump
51. backflush selonoid
52. backflush saline reservoir
53. drip event sensor
FIG. 6: A drawing showing the acoustic wave generating element. A
moving coil NXT excitor is shown 54.
The following description is related to embodiments of the
invention in which the fluids are sequentially moved across the
filter:
In normal operation the filter unit is free of fluid. The
back-flushing pump is switched on to deliver fluid into the lower
chamber of the filtration unit 10 until fluid passes through the
filter 11 and into the upper (pre-filtration) chamber. The acoustic
element has an amplitude in the range 4.2V through 7.36V peak to
peak and a frequency range 300 to 700 Hz. The element is set to
drive a standing wave through the fluid and the fluid is observed
to be in constant agitation. The vacuum pump is switched on to draw
the fluid level down just to the point of passage across the
filter. The flow-rate across the filter is adjusted accordingly by
a needle valve 20. The sample fluid is delivered to the upper
(pre-filtration) chamber and is observed to be in constant
agitation. The cyclic process of rapid back-flushing and vacuum
draw to slowly reduce the sample volume is initiated from the PLC.
The sample volume is reduced typically by 10-fold and the process
is stopped from the PLC. The sample volume is removed from the
upper (pre-filtration) chamber.
FIG. 7 illustrates a filter holder for use in the apparatus of the
present invention. The design of the filter holder permits movement
of the filter in a lateral or vertical direction or a combination
thereof. The holder 55 is substantially circular. A
horseshoe-shaped or U-shaped aperture 56 splits the holder into two
portions, an outer annular portion 57 and a central circular island
58. Portion 57 is connected to portion 58 by bridge elements 59a
and 59b. Portion 58 is provided with a plurality of pores. The
pores are distributed in a uniform pattern. The pores are
substantially circular having a diameter of about 3 microns. A pin
element 60 is provided on the outer surface of portion 57 in line
with bridge element 59b. This pin element 60 is mechanically driven
by a motor and cam (not shown) which are exterior to the
apparatus.
The combined filter holder and filter are manufactured as a single
plastic unit.
Examples of Separation of a Solid Fraction from a Fluid Sample
1. Human Bone Marrow Aspirate Samples
Human bone marrow aspirate was obtained commercially from Cambrex
before use they were passed through a 70 .mu.m cell strainer to
remove any adipocytes and large cell aggregates. The white blood
cells (WBC) and red blood cells (RBC) were counted using the
coulter counter. 2 mls of cell suspension was added into the device
which had been loaded with a photo-electroformed mesh, acting as
the filter having a pore size about .about.3 .mu.m. The separation
process was initiated using the control unit of the device and
continued until a concentrated fluid fraction of approximately 200
.mu.l remained upstream of the filter in the upper chamber of the
device. Post-processing, 100 .mu.l of the concentrate was removed
from on top of the filter in the device and then passed through the
coulter counter which was calibrated to daily standards before each
experiment. The resulting WBC and RBC counts in the sample were
obtained.
2. Porcine Bone Marrow Samples
Isolation and Culture-Expansion of Porcine Cell Populations
Fresh porcine hind limbs were collected from an abattoir.
Trabeculum bone marrow was extracted from the femoral head of each
leg and collected into pots containing PBS. The marrow was minced
finely using scissors and the resulting slurry was left to agitate
on an orbital shaker at 37.degree. C./5% CO.sup.2, after this the
supernatant was passed through 70 .mu.m cell strainer into separate
tubes. The tubes were then spun at 1500 rpm for 5 minutes and the
supernatant discarded, the resulting pellets were re-suspended in
10 ml of .alpha.-MEM+15% FCS media.
Bone marrow was isolated and processed as above, 100 .mu.l of the
bone marrow suspension was then passed through the coulter counter
which was calibrated to daily standards before each experiment. The
resulting WBC and RBC counts obtained were used to bring the WBC of
the bone marrow extract to 1.times.10.sup.7 cells per ml by
diluting the extract with porcine plasma. 2 mls of this fluid was
added to the device for separation.
Preparation of Porcine Plasma
Fresh porcine blood was collected from an abattoir in a storage
bottle that contained sodium citrate tribasic solution 4% (w/v)
(Sigma) at a ratio of 1:9 (sodium citrate to blood). The blood was
aliquoted into 50 ml falcon tubes and spun at 2500 rpm for 30
minutes and the supernatant carefully transferred to another falcon
tube. The supernatant was spun again at 2500 rpm for 30 minutes and
the supernatant transferred to a new 50 ml falcon tube, and stored
at -20.degree. C. until ready for use.
Ficoll Separation of Porcine Bone Marrow Aspirate
Bone marrow was extracted from a fresh porcine hind limb as
previously described, and the final cell pellet was re-suspended in
25 mls of .alpha.-MEM+15% FCS media.
Fresh porcine blood, was diluted with phosphate buffered saline, to
bring the number of RBC down to roughly 3.5.times.10.sup.9 cells
per ml. Once this was done the number of WBC was increased to
roughly 2.5.times.10.sup.7 cells per ml; by adding the bone marrow
obtained earlier. The blood was then diluted 2:1 (balanced salt
solution: blood) and then 35 mls of this diluted blood was then
layered on top of 15 mls of Ficoll (Amersham biosciences). The
tubes were then spun at 1800 rpm for 30 minutes with the brake
switched off. (Megafuge 1.0R SOP/CB/021.). The WBC layer was then
extracted and pelleted down and resuspended in low glucose DMEM
media and counts performed on both the RBC and WBC products.
3. Porcine Blood Samples
Fresh porcine blood was collected from an abattoir in a storage
bottle that contained sodium citrate tribasic solution 4% (w/v) at
a ratio of 1:9 (sodium citrate to blood). Typically, a 20 ml
aliquot of this was passed through a 70 .mu.m cell strainer into a
collection tube. This process was repeated three times using a
fresh strainer in each pass. 2 mls of the final strained sample was
added to the device for separation.
Results
FIG. 8: A filter having a pore size of about 3 microns is
demonstrated as being optimal (p<0.05) in recovering MNCs from
whole porcine blood: Statistical test utilized is the one-way ANOVA
with Tukey post-hoc analysis and a 95% confidence interval.
FIG. 9 illustrates that MNCs from whole porcine blood can be
enriched over 6-fold within 6 minutes when a filter having a pore
size of about 3 microns is used.
FIG. 10 illustrates that that a volume reduction of porcine bone
marrow tissue of about 10-fold is attainable when the operational
conditions used in the apparatus combine: (i) a vacuum drawing the
fluid sample downwards through the filter, (ii) a backwash forcing
the washing fluid upwards through the filter, and (iii) an acoustic
element that generates and transmits a standing wave upwards
through the washing fluid and the sample fluid.
FIG. 11 the optimal flow rate of fluid through the filter was
determined. The fluid sample was derived from porcine marrow. The
pre-filtration fluid sample volume was 2 ml. The post-filtration
fluid sample volume was 200 .mu.l. Time to achieve this reduction
in fluid sample volume was 8 mins at 6 drops/min, 4 mins at 12
drops/min and 2 mins at 25 drops/min all using 3 micron mesh
filter. The optimal flow-rate was found to be 6 drops/min as this
corresponds to an improved enrichment of MNCs in the concentrated
fluid sample when compared to a flow rate of 12 drops/min or 25
drops/min.
FIG. 12 illustrates the enrichment of WBCs compared to RBCs within
the fluid sample post-filtration. A figure of less than 1 is
indicative of RBCs passing through the filter.
FIG. 13 illustrates the ratio of RBC:WBC in a whole porcine blood
sample pre- and post-filtration. Pre-filtration the ratio of
RBC:WBC is about 375:1. Post-filtration the ratio of RBC:WBC is
about 50:1.
FIG. 14 illustrates the fold concentration of marrow nucleated
cells and the % retention of marrow nucleated cells from human bone
marrow using a PET filter having a thickness of 23 .mu.m, pore
density of 400 k and a pore size of 3.5 .mu.m.
FIG. 15 illustrates the distribution of pore size on a PET filter
having a pore density of 400,000. The figure further illustrates
the performance of this filter when considering the processing
cells from a bone marrow aspirate.
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